Visual tags, such as barcodes, can be used to store information in the form of bits that are encoded into corresponding visual elements. Such stored information may include data that define one or more actions to be performed by a mobile device. In addition, this stored information may include error correction information and/or error detection information (e.g., checksums).
A mobile device having an image sensor (for example, a camera phone) can read a visual tag's information and carry out the actions defined by this information. Visual tags are not the only articles that may trigger a mobile device's actions. In a similar manner, radio frequency identification (RFID) tags, audio streams (also called audio tags), watermarks in visual media, and the like can be used to trigger actions in mobile devices with corresponding sensors.
Such tag-initiated actions can be, for example, instructions regarding the storage of calendar events, contact information, or other information in the device's memory. In addition, examples of tag-initiated actions include launching an external communications connection (e.g., placing a phone call, sending an SMS message, initiating a wireless application protocol session, or establishing a web connection). Also, tag-initiated actions may include a device launching an application and passing tag-originated parameters to the application. Further, such actions may result in the mobile device obtaining services or content from remote providers.
The triggering of such actions in mobile devices can be achieved by encoding the action defining data according to a language developed for that particular purpose. Such languages (referred to herein as action languages) define how particular actions are indicated and how the data is to be interpreted.
The amount of information that a tag may store is often limited. For instance, the number of bits expressed in a visual tag determines the visual tag's physical size. However, this size cannot become too large because limits exist in the size of most associated media channels (e.g., space available in a newspaper advertisement). Audio tags are similarly constrained as the transmission speed of an audio channel is relatively low due to noisy environments. Therefore, it is desirable for such action languages to minimize the number of symbols (e.g., bits) required to express the action.
Archiver data compression techniques, such as zip, arj, and lhz, compress data by identifying data sequence patterns and replacing them with indices from a compression dictionary. However, such compression techniques are not suitable for small amounts of data, at least because the compression dictionary must accompany the compressed data. Thus, the employment of such compression techniques with tags may result in “compressed data” that is actually larger than the original data.
Also several languages exist for inputting data into mobile devices. VCal and VCard are examples of such languages. However, these textual languages are quite verbose and do not provide for efficient information storage in tags. An additional example of such languages is the wireless application protocol (WAP) binary extensible markup language (XML). This language merely defines compacting methods for data identifiers. In other words, it replaces the long, textual parameter and action titles with shorter titles. However, this language does not compress the parameters themselves.